Method for manufacturing thin film oxide superconductors and superconductor devices by x-ray irradiation

Abstract

A manufacturing method for the thin film superconductor is disclosed in which photons having energies larger than ultraviolet rays are irradiated to the thin film superconductor on or after formation of the thin film. Further, manufacturing methods for superconductive magnetic memory, Josephson device and superconductive transistor are disclosed.

What is claimed is: 
     
       1. A method for manufacturing a thin film P-type oxide superconductor element which comprises: providing an oxide superconductor thin film in which a critical current density obtained from a magnitude of diamagnetization measured at 48 K. in an outer magnetic field of 150 Oe is more than 3 mill.A/cm 2  and the critical current density obtained from a transport current measured at 48 K. in a null magnetic field is more than 3 mill.A/cm 2  by forming an oxide superconductor thin film on a substrate and irradiating said oxide superconductor thin film with photons having energies larger than that of ultraviolet rays and   forming a weak coupling portion on said thin film oxide superconductor by irradiating photons having energies larger than that of ultraviolet rays onto a minute portion of said thin film to form a structure wherein said thin film oxide superconductor is divided into at least two regions by said weak coupling portion.   
     
     
       2. A method for manufacturing a Josephson device which comprises: providing a P-type oxide superconductor thin film in which a critical current density obtained froom a magnitude of diamagnetization measured at 48 K. in an outer magnetic field of 150 Oe is more than 3 mill.A/cm 2  and a critical current density obtained from the transport current measured at 48 K. in a null magnetic field is more than 3 mill.A/cm 2  by forming a thin film oxide superconductor on a substrate and irradiating said thin film with photons having energies larger than that of ultraviolet rays, and   selectively oxidizing two regions on said thin film oxide superconductor which are separated by a minute gap portion to form a junction portion in said oxide superconductor thin film.   
     
     
       3. The method for manufacturing a Josephson device in accordance with claim 2 which comprises using a mask pattern for forming said junction portion, and employing as said mask pattern an electron beam resist made of an acrylic resin or styrene resin or a negative resist for optolithography. 
     
     
       4. The method for manufacturing a Josephson device according to claim 2 wherein said oxidating step is performed by irradiation of oxygen ions or quasi-stabilized oxygen atoms is an excited state. 
     
     
       5. The method for manufacturing a Josephson device in accordance with claim 2 wherein said oxidizing step is performed using a gas containing ozone. 
     
     
       6. A method for manufacturing a Josephson device which comprises selectively irradiating photons having energies larger than that of ultraviolet rays only onto two regions which are separated by a minute gap portion of P-type thin film oxide superconductor in which a critical current density obtained froim a magnitude of diamagnetization measured at 48 K. in an outer magnetic field of 150 Oe is more than 3 mill.A/cm 2  and a critical current density obtained from the transport current measured at 48 K. in a null magnetic field is more than 3 mill.A/cm 2  by forming a thin film oxide superconductor on a substrate and irradiating said thin film with photons having energies larger than that of ultraviolet rays, and oxidizing a surface of the oxide superconductor thin film during said irradiating step or after said irradiating. 
     
     
       7. A method for manufacturing an oxide superconductor transistor, the oxide superconductor transistor including a gate electrode formed on a surface of a channel region with a gate insulating film interposed therebetween, and a superconductor source region and a superconductor drain region each comprising a strong superconductor in which a critical current density obtained from a magnitude of diamagnetization measured at 48 K. in an outer magnetic field of 150 Oe is more than 3 mill.A/cm 2  and the critical current density obtained from a transport current measured at 48 K. in a null magnetic field is more than 3 mill.A/cm 2 , said method comprising: forming an oxide superconductor thin film on a substrate,   forming a gate isulating film and a gate electrode on a surface portion of said oxide superconductor thin film corresponding to said channel region, and   irradiating photons having energies larger than that of ultraviolet rays onto said oxide superconductor thin film using said gate electrode as a mask and oxidizing said superconductor thin film during or after said irradiating step, thereby improving crystallinity in the superconductor source area and superconductor drain area and concurrently forming the channel layer.   
     
     
       8. The method for manufacturing an oxide superconductor transistor in accordance with claim 7, comprising forming the gate electrode of a metal or a silicide. 
     
     
       9. A method for manufacturing an oxide superconductor magnetic memory which is capable of distinguishing memory states responsive to an absolute value of magnetization and which includes at least one strong superconductor in which the critical current density obtained from a magnitude of diamagnetization measured at 48 K. in an outer magnetic field of 150 Oe is more than 3 mill.A/cm 2  and a critical current density obtained from the transport current measured at 48 K in a null magnetic field is more than 3 mill.A/cm 2  and at least one weak superconductor having a critical current density smaller than that of said strong superconductor, said method comprising preparing said strong superconductor by irradiating a thin film oxide superconductor with photons having energies larger than that of ultraviolet rays accompanied by oxidation, and preparing said weak superconductor by only irradiating the thin film oxide superconductor with photons having energies larger that that of ultraviolet rays.